1. Field of the Invention
This invention relates generally to on-line computer control systems and more particularly to such systems including a programing console for selectively altering input and output data in a computer or controller for controlling process equipment while the system is on-line.
2. Description of the Prior Art
Process control computers for on-line control of process equipment have been in use for a number of years. Most recently, programmable controllers have come into use for controlling various process equipments of the type heretofore controlled by conventional relay logic controllers. The programmable controller replaces those conventional controllers by the use of a program in its memory which simulates the relay logic inherent in relay type controllers. The program performs its control function by directing the reading of input conditions in the form of signals from the process equipment into the controller memory, performing logical operations on those conditions in accordance with the simulated relay logic, and sending output conditions in the form of control signals to the equipment.
Occasions arrive in process control systems when it is desirable to override or force those input and output conditions to an opposite state. One occasion is when trouble-shooting a malfunctioning system to isolate the location of some inoperable or abnormally operating device. Other occasions arise when the forcing or overriding of signals is desirable, such as during the start-up of a new system when debugging software and hardware is normally required.
To the best of this inventor's knowledge this forcing and overriding of signals has always been done in prior systems by the physical placement of a jumper wire directly on a terminal connector or the likeand connecting the jumper to a suitable potential. This connection of jumpers is a timed consuming task. Further, it is frequently difficult to connect a jumper because of the inaccessibility to the equipment. Additionally, the placement of jumpers on equipment can create systems problems, particularly if they are inadvertently left in the equipment. This can be troublesome if a new maintenance man is assigned to the system with no knowledge of the existence of the jumpers.
It is therefore desirable to provide a programmable controller system or the like for on-line control of process equipment which provides an instant and easy means and method of forcing or overriding input and output conditions of the system whereby a maintenance operator of the system need make no physical jumper wire connections to effect the forcing and whereby indication is always given of the presence of a forced or overriding condition.